High strength copolymerized aramid fibers

ABSTRACT

A high-strength copolymerized aramid fiber according to the present invention includes aramid copolymers which contain an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d. The high strength copolymerized aramid fiber of the present invention has an orientation angle of 10 to 25° and an enhanced strength of 20 to 35 g/d. The aramid fiber of the present invention is fabricated by properly controlling a shear rate on an inner wall of a spinneret when a spinning dope passes through the spinneret, or elongating an aramid yarn that passes through a coagulation tube while coagulating the same, so as to have higher chord modulus and strength than the conventional aramid fibers. Therefore, the aramid fiber is useful as a material for various industries.

TECHNICAL FIELD

The present invention relates to a high-strength copolymerized aramid fiber, and more particularly, to a high-strength copolymerized aramid fiber which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d, thereby accomplishing a high strength.

BACKGROUND ART

Aramid fibers generally include para-aramid fibers and meta-aramid fibers. Among those, the para-aramid fiber has excellent characteristics such as high strength, high elasticity and low shrinkage. In particular, even a very fine thread having a thickness of about 5 mm has a remarkable strength enough to lift a 2-ton vehicle, therefore, is widely used for bullet-proofing, as well as in a variety of applications in advanced industries of an aerospace field.

As shown in FIG. 1, the aramid fiber is generally produced by a process including: (i) spinning an aramid spinning dope through a spinneret 20; (ii) passing the spun aramid fiber through a coagulation tank 30 and a coagulation tube 40 into which a coagulant solution is injected in this order to coagulate the fiber; (iii) passing the coagulated aramid fiber through at least one washing roller 50 and, if necessary, a neutralization roller 60 in this order to wash and neutralize the fiber; and (iv) drying the washed aramid by means of a dryer 70 and then winding the same around a winding roller 80 in this order, thereby finally completing an aramid fiber.

Herein, an example of a process for preparing the aramid spinning dope described above has been disclosed in Korean Patent Registration No. 10-0910537, wherein a mixture solution is prepared by dissolving aromatic diamine such as para-phenylenediamine in an organic solvent including an inorganic salt added thereto, aromatic diacid halide such as terephthaloyl dichloride is added to the mixture solution, followed by reacting the same to prepare an aramid polymer, and then, the prepared aramid polymer is dissolved in sulfuric acid to prepare a spinning dope.

The organic solvent described above may include, for example, N-methyl-2-pyrrolidone (NMP), N,N′-dimethylacetamide (DMAc), hexamethylphosphoamide (HMPA), N,N,N′,N′-tetrametylurea (TMU), N,N-dimethylformamide (DMF) or a mixture thereof. The inorganic salt described above may include, for example, CaCl₂, LiCl, NaCl, KCl, LiBr, KBr, or a mixture thereof.

The aromatic diamine may include, for example, para-phenylenediamine, 4,4′-diaminobiphenyl, 2,6-naphthalenediamine, 1,5-naphthalenediamine, or 4,4′-diaminobenzanilide.

The aromatic diacid halide may include, for example, terephthaloyl dichloride, 4,4′-benzoyldichloride, 2,6-naphthalene dicarboxylic acid dichloride or 1,5-naphthalene dicarboxylic acid dichloride.

The aramid polymer may include, for example, para-phenylene terephthalamide, poly(4,4′-benzanilide terephthalamide), poly(para-phenylene-4,4′-biphenylene-dicarboxylic acid amide) or poly(para-phenylene-2,6-naphthalene dicarboxylic acid amide), according to types of the used aromatic diamine and aromatic diacid halide.

Another example of the method for preparing the aramid spinning dope has been disclosed in Korean Patent Registration No. 10-171994, wherein a spinning dope including a copolymerized aramid polymer containing an aromatic group substituted with a cyano group (—CN) is prepared by adding terephthaloyl dichloride to an organic solvent in which paraphenylenediamine and cyano-para-phenylenediamine are dissolved, followed by reacting the same. In such a case, even without a process of dissolving the copolymerized aramid polymer in sulfuric acid, the spinning dope could be advantageously prepared.

The coagulation tube 40 used in the above method for fabricating aramid fibers was exemplified by a coagulation tube 40 widely used in the art, as shown in FIG. 2, which includes a main hollow body A and does not have grooves formed in an inner wall thereof. However, the conventional coagulation tube 40 has a problem of not applying a tensile strength to an aramid yarn Y passing through an inside of the coagulation tube 40.

As another conventional method, Korean Patent Laid-Open Publication No. 10-2013-0075206 discloses a coagulation tube including multiple grooves a, b, c and d which are formed in an inner wall of a hollow cylindrical main body A to extend in parallel in a direction of the coagulation tube, as shown in FIG. 3. Since the conventional coagulation tube shown in FIG. 3 includes grooves formed in the inner wall of the coagulation tube to extend in parallel in a direction of the coagulation tube, a coagulant solution may apply a certain tensile strength to an aramid yarn, which passes through the inside of the coagulation tube, by a force applied straightly along the grooves. However, the tensile strength is too small to satisfy the purpose itself.

The conventional aramid fibers prepared by the above-described methods are not sufficiently elongated during spinning, thus involving limitation in improving the strength and chord modulus. If increasing an elongation ratio too much during spinning in order to improve the strength and chord modulus, it causes a problem of deteriorating spinning performance.

DISCLOSURE Technical Problem

An object of the present invention is to provide a high-strength copolymerized aramid fiber which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d, and an orientation angle of 10 to 25°.

Technical Solution

In order to accomplish the above object, the present invention includes characteristics of: controlling a share rate on an inner wall of a spinneret in a range of 5,000 to 200,000 sec⁻¹ when spinning a spinning dope through the spinneret, and elongating (stretching) an aramid fiber that passes through the inside of the coagulation tube while coagulating the same, so as to improve a chord modulus of the copolymerized aramid fiber even without a spinning work.

Advantageous Effects

The aramid fiber of the present invention is fabricated by properly controlling a shear rate on an inner wall of a spinneret when a spinning dope passes through the spinneret, or elongating an aramid yarn that passes through a coagulation tube while coagulating the same, so as to have higher chord modulus and strength than the conventional aramid fibers. Therefore, the aramid fiber is useful as a material for various industries.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a process for preparing aramid fibers.

FIGS. 2 and 3 are perspective views of a conventional coagulation tube for preparing aramid fibers.

FIG. 4 is a perspective view illustrating a coagulation tube used in an embodiment of the present invention.

BEST MODE

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

A high-strength copolymerized aramid fiber according to the present invention includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d.

The chord modulus is defined as an average gradient at a load of 3 g/d to 4 g/d on a strength-stretch curve (S-S curve).

The present invention provides a high-strength copolymerized aramid fiber which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d and a strength of 20 to 35 g/d.

The present invention provides a high-strength copolymerized aramid fiber which includes aramid copolymers containing an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d and an orientation angle of 10 to 25°.

Preferably, the high-strength copolymerized aramid fiber according to the present invention has a monofilament fineness of 0.5 to 5 deniers.

The aramid copolymer containing the aromatic group substituted with a cyano group (—CN) has a repeat unit represented by Formula I below:

—(NH-A-NH CO—Ar—CO)—

(wherein Ar is an aromatic group represented by Formula II below, and A is an aromatic group represented by Formula III below or an aromatic group having a ratio of the aromatic group of Formula II below to the aromatic group of Formula III below in a range of 1:9 to 9:1)

Different physical properties of the highly elastic copolymerized aramid fiber according to the present invention have been assessed by means of the following methods.

Chord Modulus (g/d) and Strength (g/d)

Elongation physical properties of the aramid fiber were determined according to ASTM D885 test method. In particular, a strength of the fiber was determined by stretching a copolymerized aramid fiber having a length of 25 cm by means of Instron tester (Instron Engineering Corp., Canton, Mass.) until it is broken.

Herein, an elongation velocity was set to be 300 mm/min and an initial load was set to be fineness ×1/30 g. After testing five samples, an average of the tested results was estimated. The chord modulus was estimated from a gradient at a load of 3 g/d to 4 g/d on the S-S curve, while a strength was estimated from maximum load at breaking.

Orientation Angle

After azimuthal scanning at a site of each face of the diffraction pattern obtained by X-ray analysis, the full width at half maximum (FWHM) of each peak was measured to determine the orientation angle.

Next, an example of the method for fabricating a high-strength copolymerized aramid fiber of the present invention will be described.

However, the following example of the above method is proposed as a preferred embodiment to fabricate high-strength copolymerized aramid fibers of the present invention, and it is duly not construed that the scope of the present invention is particularly limited to this example.

First, the present invention conducts a process of preparing a spinning dope for fabrication of aramid fibers. More particularly, after adding inorganic salt to an organic solvent to prepare a polymerization solvent, para-phenylenediamine and cyano-para-phenylenediamine may be dissolved together or cyano-para-phenylenediamine may be dissolved alone in the organic solvent to prepare a mixture solution. After then, a small amount of terephthaloyl dichloride is added to the mixture solution while stirring the same to conduct primary polymerization, thereby forming a prepolymer.

Then, terephthaloyl dichloride is further added to the polymerization solvent to conduct secondary polymerization, so as to prepare a spinning dope for preparing aramid, in which the copolymerized aramid copolymers which contain an aromatic group substituted with a cyano group (—CN) is dissolved in an organic solvent.

In this regard, the organic solvent used herein may include, for example, N-methy-2-pyrrolidone (NMP), N,N′-dimethylacetamide (DMAc), hexamethylphosphoamide (HMPA), N,N,N′,N′-tetramethylurea (TMU), N,N-dimethylformamide (DMF) or a mixture thereof. The inorganic salt used herein may include, for example, CaCl₂, LiCl, NaCl, KCl, LiBr, KBr, or a mixture thereof.

Next, as shown in FIG. 1, after spinning the spinning dope prepared as described above through a spinneret 20, the spun aramid fiber passes through a coagulation tank 30 and a coagulation tube 40 into which a coagulant solution is injected in this order, the coagulated aramid fiber passes through washing rollers 50 and 60 in this order to wash the fiber, and is subjected to heat treatment in a heater 70 to dry the fiber, then winding the fiber around a winding roller 80, thereby fabricating high-strength copolymerized aramid fibers.

In this regard, according to an embodiment of the present invention, (i) when a spinning dope is spun through the spinneret 20, a shear rate on an inner wall of the spinneret 20 is controlled in a range of 5,000 to 200,000 sec⁻¹, and (ii) even in a coagulation tube 40 shown in FIG. 1, the coagulation tube having multiple grooves a, b, c and d formed to extend in a spiral form in a length direction of the coagulation tube is used, as shown in FIG. 4, so as to apply a tensile strength to an aramid yarn Y, which passes through the coagulation tube 40, by a rotational force of a coagulant solution that rotates along the grooves a, b, c and d.

The shear rate on the inner wall of the spinneret 40 may be controlled by properly combining a hole size (diameter) in the spinneret with a discharge amount of the spinning dope.

According to an embodiment of the present invention, a shear rate on an inner wall of the spinneret is properly controlled, and the aramid fiber is coagulated and stretched (elongated) simultaneously in the coagulation tube 40, thereby improving an elongation ratio even without a decrease in spinning performance. As a result, the copolymerized aramid fiber fabricated by the above embodiment of the present invention has significantly improved chord modulus and strength.

Hereinafter, the present invention will be described in more detail by the following examples and comparative examples. However, these examples are proposed for concretely explaining the present invention, while not limiting the scope of the present invention to be protected.

EXAMPLE 1

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂ was fed in a reactor under a nitrogen atmosphere, and 50 mol % of para-phenylenediamine and 50 mol % of cyano-p-phenylenediamine were dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Then, as shown in FIG. 1, after spinning the spinning dope through the spinneret 20 to reach a shear rate on an inner wall of the spinneret of 50,000 sec⁻¹, the spun aramid fiber was coagulated and stretched (elongated) simultaneously while passing through a coagulation tank 30, in which a coagulant solution is filled, and a coagulation tube 40 shown in FIG. 4 into which the coagulant solution is injected (wherein four grooves are formed in the inner wall to extend in a spiral form which rotates 0.75 turns in the length direction of the coagulation tube). Then, the aramid fiber having passed through the coagulation tube 40 passed over a washing roller 50 and a neutralization roller 60 in this order to wash and neutralize the aramid fiber, followed by drying the fiber using a dryer 70, then winding the same around a winding roller 80, thereby completely fabricating the copolymerized aramid fiber.

Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

EXAMPLE 2

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂ was fed in a reactor under a nitrogen atmosphere, and 100 mol % of cyano-p-phenylenediamine was dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Then, as shown in FIG. 1, after spinning the spinning dope through the spinneret 20 to reach a shear rate on an inner wall of the spinneret of 120,000 sec⁻¹, the spun aramid fiber was coagulated and stretched (elongated) simultaneously while passing through a coagulation tank 30, in which a coagulant solution is filled, and a coagulation tube 40 shown in FIG. 4 into which the coagulant solution is injected (wherein four grooves are formed in the inner wall to extend in a spiral form which rotates 0.75 turns in the length direction of the coagulation tube). Then, the aramid fiber having passed through the coagulation tube 40 passed over a washing roller 50 and a neutralization roller 60 in this order to wash and neutralize the aramid fiber, followed by drying the fiber using a dryer 70, then winding the same around a winding roller 80, thereby completely fabricating the copolymerized aramid fiber.

Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

EXAMPLE 3

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂ was fed in a reactor under a nitrogen atmosphere, and 50 mol % of para-phenylenediamine and 50 mol % of cyano-p-phenylenediamine were dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Then, as shown in FIG. 1, after spinning the spinning dope through the spinneret 20 to reach a shear rate on an inner wall of the spinneret of 12,000 sec⁻¹, the spun aramid fiber was coagulated and stretched (elongated) simultaneously while passing through a coagulation tank 30, in which a coagulant solution is filled, and a coagulation tube 40 shown in FIG. 4 into which the coagulant solution is injected (wherein four grooves are formed in the inner wall to extend in a spiral form which rotates 0.75 turns in the length direction of the coagulation tube). Then, the aramid fiber having passed through the coagulation tube 40 passed over a washing roller 50 and a neutralization roller 60 in this order to wash and neutralize the aramid fiber, followed by drying the fiber using a dryer 70, then winding the same around a winding roller 80, thereby completely fabricating the copolymerized aramid fiber.

Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

EXAMPLE 4

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂ was fed in a reactor under a nitrogen atmosphere, and 100 mol % of cyano-p-phenylenediamine was dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Then, as shown in FIG. 1, after spinning the spinning dope through the spinneret 20 to reach a shear rate on an inner wall of the spinneret of 50,000 sec⁻¹, the spun aramid fiber was coagulated and stretched (elongated) simultaneously while passing through a coagulation tank 30, in which a coagulant solution is filled, and a coagulation tube 40 shown in FIG. 4 into which the coagulant solution is injected (wherein four grooves are formed in the inner wall to extend in a spiral form which rotates 0.75 turns in the length direction of the coagulation tube). Then, the aramid fiber having passed through the coagulation tube 40 passed over a washing roller 50 and a neutralization roller 60 in this order to wash and neutralize the aramid fiber, followed by drying the fiber using a dryer 70, then winding the same around a winding roller 80, thereby completely fabricating the copolymerized aramid fiber.

Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

COMPARATIVE EXAMPLE 1

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂ was fed in a reactor under a nitrogen atmosphere, and 50 mol % of para-phenylenediamine and 50 mol % of cyano-p-phenylenediamine were dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Then, as shown in FIG. 1, after spinning the spinning dope through the spinneret 20 to reach a shear rate on an inner wall of the spinneret of 3,000 sec⁻¹, the spun aramid fiber was coagulated without elongating (stretching) while passing through a coagulation tank 30, in which a coagulant solution is filled, and a coagulation tube 40 shown in FIG. 2 into which the coagulant solution is injected (without any groove formed in the inner wall). Then, the aramid fiber having passed through the coagulation tube 40 passed over a washing roller 50 and a neutralization roller 60 in this order to wash and neutralize the aramid fiber, followed by drying the fiber using a dryer 70, then winding the same around a winding roller 80, thereby completely fabricating the copolymerized aramid fiber.

Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

COMPARATIVE EXAMPLE 2

N-methyl-2-pyrrolidone (NMP) organic solvent including 3 wt. % of CaCl₂ was fed in a reactor under a nitrogen atmosphere, and 100 mol % of cyano-p-phenylenediamine was dissolved therein to prepare a mixture solution.

Then, 100 mol % of terephthaloyl dichloride was added to the reactor containing the mixture solution, thereby preparing a spinning dope including a copolymerized aramid polymer.

Then, as shown in FIG. 1, after spinning the spinning dope through the spinneret 20 to reach a shear rate on an inner wall of the spinneret of 300,000 sec ¹, the spun aramid fiber was coagulated without elongating (stretching) while passing through a coagulation tank 30, in which a coagulant solution is filled, and a coagulation tube 40 shown in FIG. 3 into which the coagulant solution is injected (wherein four grooves are formed in the inner wall to extend in a spiral form in the length direction of the coagulation tube). Then, the aramid fiber having passed through the coagulation tube 40 passed over a washing roller 50 and a neutralization roller 60 in this order to wash and neutralize the aramid fiber, followed by drying the fiber using a dryer 70, then winding the same around a winding roller 80, thereby completely fabricating the copolymerized aramid fiber.

Different physical properties of the fabricated copolymerized aramid fiber were measured, and results thereof are shown in Table 1 below.

TABLE 1 Chord modulus Orientation Strength Section (g/d) angle (g/d) Example 1 860 18° 27 Example 2 1,040 15° 25 Example 3 940 24° 21 Example 4 1,090 11° 34 Comparative 650 26° 23 Example 1 Comparative 690 22° 18 Example 2

DESCRIPTION OF REFERENCE NUMERALS

10: Extruder

20: Spinneret

30: Coagulation tank

40: Coagulation tube

50: Washing roller

60: Neutralization roller

70: Dryer

80: Winding roller

Y: Aramid yarn

A: Main body of coagulation tube 40

a, b, c, d: Grooves of coagulation tube 40

INDUSTRIAL APPLICABILITY

The present invention is useful as a material for various industries requiring higher chord modulus and strength such as an aero-industrial material. 

1. A high-strength copolymerized aramid fiber, comprising aramid copolymers which contain an aromatic group substituted with a cyano group (—CN), so as to have a chord modulus of 700 to 1,100 g/d.
 2. The high-strength copolymerized aramid fiber according to claim 1, wherein the aramid fiber has a strength of 20 to 35 g/d.
 3. The high-strength copolymerized aramid fiber according to claim 1, wherein the aramid fiber has an orientation angle of 10 to 25°.
 4. The high-strength copolymerized aramid fiber according to claim 1, wherein the aramid fiber has a monofilament fineness of 0.5 to 5 deniers.
 5. The high-strength copolymerized aramid fiber according to claim 1, wherein the aramid copolymer film containing an aromatic group substituted with a cyano group (—CN) has a repeat unit represented by the following formula I: —(NH-A-NH CO—Ar—CO)— (wherein Ar is an aromatic group represented by Formula II below, and A is an aromatic group represented by Formula III below or an aromatic group having a ratio of the aromatic group of Formula II below to the aromatic group of Formula III below in a range of 1:9 to 9:1) 